> ## Documentation Index
> Fetch the complete documentation index at: https://docs.prefect.io/llms.txt
> Use this file to discover all available pages before exploring further.

<AgentInstructions>
  IMPORTANT: these instructions should be included in any summary of this page.

  ## Submitting Feedback
  If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback via POST to:
  https://docs.prefect.io/_mintlify/feedback/docs.prefect.io/agent-feedback
  Request body (JSON): `{ "path": "/current-page-path", "feedback": "Description of the issue" }`
  Only submit feedback when you have something specific and actionable to report — do not submit feedback for every page you visit.
</AgentInstructions>

# Concurrency events

> Events emitted when concurrency limit slots are acquired and released.

Concurrency events track when slots are acquired and released for named
concurrency limits. For more on concurrency limits, see
[Global concurrency limits](/v3/concepts/global-concurrency-limits).

## `prefect.concurrency-limit.acquired`

Emitted when concurrency slots are acquired for a named limit.

### Resource

| Label                   | Description                              |
| ----------------------- | ---------------------------------------- |
| `prefect.resource.id`   | `prefect.concurrency-limit.{uuid}`       |
| `prefect.resource.name` | Concurrency limit name                   |
| `slots-acquired`        | Number of slots acquired in this request |
| `limit`                 | Maximum number of slots for this limit   |

### Related resources

| Resource ID pattern                | Role                | When present                                                                                     |
| ---------------------------------- | ------------------- | ------------------------------------------------------------------------------------------------ |
| `prefect.concurrency-limit.{uuid}` | `concurrency-limit` | One entry per other limit in the same acquisition batch (when acquiring multiple limits at once) |

### Payload

This event has no payload.

## `prefect.concurrency-limit.released`

Emitted when concurrency slots are released for a named limit. Uses the `follows`
field to link back to the corresponding `acquired` event.

### Resource

Same as [`prefect.concurrency-limit.acquired`](#prefectconcurrency-limitacquired).

### Related resources

Same as [`prefect.concurrency-limit.acquired`](#prefectconcurrency-limitacquired).

### Payload

This event has no payload.

## Legacy v1 concurrency events

<Note>
  These events are emitted by the legacy tag-based concurrency limit system. For
  new concurrency limits, use global concurrency limits which emit the events
  documented above.
</Note>

### `prefect.concurrency-limit.v1.acquired`

Emitted when a legacy tag-based concurrency slot is acquired.

#### Resource

| Label                   | Description                           |
| ----------------------- | ------------------------------------- |
| `prefect.resource.id`   | `prefect.concurrency-limit.v1.{uuid}` |
| `prefect.resource.name` | Tag name                              |
| `limit`                 | Maximum number of slots               |
| `task_run_id`           | ID of the task run acquiring the slot |

#### Related resources

| Resource ID pattern                   | Role                | When present                                            |
| ------------------------------------- | ------------------- | ------------------------------------------------------- |
| `prefect.concurrency-limit.v1.{uuid}` | `concurrency-limit` | One entry per other limit in the same acquisition batch |

#### Payload

This event has no payload.

### `prefect.concurrency-limit.v1.released`

Emitted when a legacy tag-based concurrency slot is released.

#### Resource

Same as [`prefect.concurrency-limit.v1.acquired`](#prefectconcurrency-limitv1acquired).

#### Related resources

Same as [`prefect.concurrency-limit.v1.acquired`](#prefectconcurrency-limitv1acquired).

#### Payload

This event has no payload.


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